The project entails several specific goals: 1. To continue the search for the precursor (s) of neurohypophysial principles through pulse-chase experiments in cultures of the hypothalamoneurohypophysial system; 2. To isolate and define the structure of the precursor(s); 3. To "clean up" remaining controversy on the one neuron-one hormone issue by applying our specific antisera in immunohistochemical studies; 4. To study the effect of various anesthetic agents on renal function, utilizing a model of chronic catheterizations in unanesthetized rats; 5. To identify -- partly by renal micropuncture -- the factors that permit the concentration of urine in the absence of VP when the aorta is constricted; 6. To determine whether medullary recycling of urea increases during the postnatal period, and to see whether such increased recycling is associated with selective postnatal development of short-looped nephrons. 7. To correlate the degree of VP-induced urinary concentration in Brattleboro homozygotes with the extent of aggregation of intramembranous particles as seen by freeze-fracture electron microscopy.